Process for preparing 1,4-butanediol

Abstract

This invention relates to a process for purifying crude 1,4-butanediol by melt crystallization and a process for preparing 1,4-butanediol by utilizing the purification process. 1,4-Butanediol is important as a material for synthesizing polyester resins, γ-butyrolactone, tetrahydrofuran, etc.

What is claimed is: 
     
       1. A process for purifying crude 1,4-butanediol comprising subjecting crude 1,4-butanediol containing impurities to melt crystallization. 
     
     
       2. A process according to claim 1, wherein said melt crystallization is carried out by a wall melt crystallization method comprising the steps of (1) obtaining 1,4-butanediol crystals by running a crude 1,4-butanediol melt on a wall cooled to or below the freezing point of 1,4-butanediol and (2) recovering 1,4-butanediol as a crystal melt by heating the wall to or above the freezing point of 1,4-butanediol crystals. 
     
     
       3. A process according to claim 1, wherein said melt crystallization is carried out by a wall melt crystallization method comprising the steps of (1) obtaining 1,4-butanediol crystals by running a crude 1,4-butanediol melt on a wall cooled to or below the freezing point of 1,4-butanediol, (2) removing the residual crude 1,4-butanediol melt from the 1,4-butanediol crystals obtained in the step (1) and heating the wall to a temperature close to the freezing point of 1,4-butanediol crystals to sweat out the impurities in the 1,4-butanediol crystals, and (3) recovering 1,4-butanediol as a crystal melt by heating the wall to or above the freezing point of 1,4-butanediol crystals obtained in the step (2). 
     
     
       4. A process according to claim 2, wherein the thickness of the crystal layer formed in the step (1) is 1 to 20 mm. 
     
     
       5. A process according to claim 3, wherein the thickness of the crystal layer formed in the step (1) is 1 to 20 mm. 
     
     
       6. A process according to any one of claims 1 to 5, wherein the crude 1,4-butanediol has a total content of impurities of 1% by weight or more. 
     
     
       7. A process according to any one of claims 1 to 5, wherein the impurity is a compound having a freezing point of not higher than 0° C. 
     
     
       8. A process according to any one of claims 1 to 5, wherein the impurity is at least one compound selected from 1,2-diacetoxybutane, 1,2-hydroxyacetoxybutane, 1,4-diacetoxybutane, 1,4-hydroxyacetoxybutane, dibutylene glycol, 2-(4'-hydroxybutoxy)tetrahydrofuran, 2-(4'-oxobutoxy) tetrahydrofuran, 1,4-di-(2'-tetrahydrofuroxy)butane, 2-methyl-1,4-butanediol, γ-butyrolactone, 2-hydroxytetrahydrofuran, and 2-methylpentanediol. 
     
     
       9. A process for purifying 1,4-butanediol comprising melt crystallizing crude 1,4-butanediol obtained by hydrolysis of diacetoxybutane. 
     
     
       10. A process for preparing 1,4-butanediol comprising (1) removing low-boiling point impurities from crude 1,4-butanediol obtained by hydrolysis of diacetoxybutane,   (2) melt crystallizing crude 1,4-butanediol obtained by the step (1) to recover 1,4-butanediol crystal melt,   (3) removing high-boiling point impurities from the mother liquor freed from the melt-crystallized 1,4-butanediol in the step (2),   (4) hydrogenating the product obtained by the step (3), and   (5) feeding the hydrogenation product back to the step (1).